Bacterial chemotaxis is a complex phenomenon in which bacterial cells can detect changes in concentrations of specific chemicals, behaviorally respond to these changes and then adapt to the new concentration of stimuli. The behavioral adaptation is associated with the reversible methylation of at least three chemotaxis specific proteins called methyl accepting chemotaxis proteins, MCPs. Our peptide mapping results suggest that MCPI and MCPII have 6 and 5 potential sites of methylation respectively. Experiments are proposed to further investigate this question and to probe the possible mechanistic role(s) of these multiple sites of methylation. In addition to methylation, the MCPs are subject to a deamidation reaction. The site of one deamidation has been identified as a glutamine residue. The resulting glutamate is a site of methylation. The physiological role of deamidation will be investigated. The chemical mechanism by which the extent of methylation of the MCPs is regulated by attractant and repellent concentrations will be investigated. Initial results suggest that the activity of the methylesterase enzyme is regulated by the level of adaptation of the cell. The regulating element may be related to the excitatory signal produced upon temporal stimulation of bacterial cells. Experiments are proposed to thoroughly investigate this point. If this interpretation is correct a direct biochemical assay of the excitatory signal may be possible.